Electromagnetic valve

ABSTRACT

There is disclosed an electromagnetic valve incorporated as the pressure medium flow regulator of an antiskid system. The valve body of the valve is connected with the magnetic armature to control the cross-sectional area of pressure medium flow through the valve in a continuous sequence proportional to the magnetic force resulting from the energizing current produced by the electronic circuitry of the antiskid system. By changing the energizing current, it is possible to change the pressure difference between the pressure medium source and the pressureoperated brake. Thus, the hydraulic antiskid control is more accurate and smoother than is achieved with previously employed open/close antiskid hydraulic control valves.

United States Patent [1 1 Belart et a1.

1 1 ELECTROMAGNETIC VALVE [75] Inventors: Juan Belart, Walldorf; WernerFink;

Dieter Kircher, both of Frankfurt; Hubertus Von Grunberg,Niederhochstadt, all of Germany [73] Assignee: lTT Industries, Inc., NewYork,

[22] Filed: Nov. 28, 1973 [21] Appl. No.: 419,846

[30] Foreign Application Priority Data Dec. 20, 1972 Germany 2262247[52-] US. Cl. 303/21 F; 303/71; 335/274 [51] Int. Cl B60! 8/02 [58]Field of Search 137/522, 596.16, 629', 303/21 F, 21 FM, 21 S, 61, 7072;335/188, 335/255,257,274

[56] References Cited UNITED STATES PATENTS 2,627,007 1/1953 Richards335/274 2,892,058 1/1959 Tancrcd 335/188 X 2,938,703 5/1960 Dietz335/274 X [451 Apr. 29, 1975 Primary ExaminerDuane A. Reger Attorney,Agent, or Firm.lohn T. OHalloran; Menotti ,1. Lombardi; Alfred C. Hill[57] ABSTRACT There is disclosed an electromagnetic valve incorporatedas the pressure medium flow regulator of an antiskid system. The valvebody of the valve is connected with the magnetic armature to control thecross-sectional area of pressure medium flow through the valve in acontinuous sequence proportional to the magnetic force resulting fromthe energizing current produced by the electronic circuitry of theantiskid system. By changing the energizing current, it is possible tochange the pressure difference between the pressure medium source andthe pressure-operated brake. Thus, the hydraulic antiskid control ismore accurate and smoother than is achieved with previously employedopen/close antiskid hydraulic control valves.

14 Claims, 6 Drawing Figures ELECTROMAGNETIC VALVE BACKGROUND OF THEINVENTION This invention relates to an electromagnetic valve for use inantiskid systems, the valve body thereof being mechanically connectedwith the magnetic armature such that the valve body blocks, opens ordiverts the passage of pressure medium flow through the valve when themagnet winding is energized.

It is a decisive factor in all antiskid systems to keep the switchingtimes of regulator-operated electromagnetic valves at a value as low aspossible. The switching times are determined, among other things, by themass of the magnetic armature and by the amount of friction to beovercome when the armature is accelerated, as well as by the magneticresistance in the closed magnetic circuit. In known plunger-typearmature valves, the plunger-type armature represents a relatively largemass. In order to provide this type of armature with a minimum amount offriction, it is necessary to provide, besides the operating air gap, aradial air gap located between the armature and the magnetic casing.

Furthermore, it is a particular desired feature in antiskid systems thatthe cross-sectional area of the valve control orifice changescontinuously and in proportion to the magnetic force in order to achievea control more accurate and smooth than could be achieved with theopen/close valves known to date.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide an electromagnetic valve which avoids the abovementioneddrawbacks, which is of simple design, easy to mount, affords rapidswitching and, if possible, permits a continuous control of thehydraulic pressure.

A feature of the present invention is the provision of anelectromagnetic valve for use in an antiskid brake system comprising amagnet housing having a first longitudinal axis, a magnet windingdisposed in the housing coaxial of the axis, a magnetic return pathdisposed in the magnet housing magnetically coupled to the winding, asleeve of non-magnetic material disposed in the return path coaxial ofthe first axis, a first chamber disposed in the magnet housing adjacentthe sleeve and the return path, a valve body disposed coaxial of thefirst axis, at least a portion of the valve body projecting into thefirst chamber, at least one armature plate disposed in the first chamberin an engaged relationship with the portion of the valve body projectinginto the first chamber, and a spring disposed in the first chamber in anengaged relationship with the valve body and the armature plate to biasthe valve body and the armature plate in a rest position, the valve bodycontrolling the flow of a brake pressure medium through the valvebetween at least a brake pressure medium inlet and a brake pressuremedium outlet when the winding is energized and the armature plate isattracted toward the return path.

Another feature of the present invention is the provision of armatureplates arranged to leave a free space for a central opening and havingtheir inner edges grip the under surface of'a collar provided directlyon the valve body or on the movable supporting member of the valve body.The armature plates are slightly inclined with their outer edgesabutting the magnetic return path.

A further feature of the present invention is the provision of adiaphragm spring provided with openings and including a centralaperture. This spring has its inner edge engaged in a groove provided onthe valve body or on the valve body support and its outer edge firmlyconnected to the housing. This spring biases both the valve body and thearmature platesin their rest positions.

Still another feature of the present invention is the provision of astar-shaped diaphragm spring having its inner edge in engagement with agroove in an annular element mounted on the valve body or on the valvebody support.

Still a further feature of the present invention is the provision thatthe characteristic curve of the diaphragm spring is adapted to thecharacteristic curve of the electromagnet.

According to another feature of this invention, the valve body is avalve slide controlling in a known manner the flow of pressure mediumbetween the connectors of the pressure-medium source of thepressureoperated device and of a pressure medium reservoir, and that thevalve slide is pressure-balanced in rest position, i.e., when there isflow of pressure medium between the pressure-medium source and thepressureoperated device.

Still a further feature of this invention is the provision of a ductinterconnecting the chambers accommodating the ends of the valve slide.

Still another feature of this invention is that the duct interconnectingthe chambers accommodating the ends of the valve slide also communicateswith the pressureoperated device in one embodiment and with the pressuremedium source in another embodiment.

A further feature of this invention is that the valve slide is dividedto form two pistons. In one embodiment, these pistons are mechanicallyconnected and pressure-balanced in rest position at their outer andinner ends by the pressure of the pressure-operated device and by thesource pressure, respectively.

In a further embodiment, the pistons forming the valve slide arepressure-balanced in rest position at their outer ends by the sourcepressure and at their inner adjacent ends by the pressure of thepressureoperated device.

In accordance with still another feature of this invention, when theelectromagnet is energized, the valve slide can be actuated by sourcepressure in a direction opposite to that of the magnetic force, and bypressure of the pressure-operated device in the direction of themagnetic force, the actuating surfaces for both pressures being of equalsize.

In accordance with a further feature of the invention, the energizingcurrent of the electromagnet and consequently the pressure differencebetween the pressure medium source and the pressure-operated device arecontinuously variable.

. BRIEF DESCRIPTION OF THE DRAWING Above-mentioned and other featuresand objects of this invention will become more apparent by reference tothe following description taken in conjunction with the accompanyingdrawing, in which:

FIG. 1 is a longitudinal cross-sectional view of a first embodiment ofan electromagnetic valve in accordance with the principles of thepresent invention showing a seat valve which is closed when the magnetcoil is deenergized;

FIG. 2 is a transverse cross-sectional view of the seat valve takenalong line A-B of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of a second embodiment ofan electromagnetic valve in accordance with the principles of thepresent invention showing a seat valve which is opened when the magnetcoil is deenergized;

FIG. 4 is a longitudinal cross-sectional view of a third embodiment ofan electromagnetic valve in accordance with the principles of thepresent invention showing a 3/2 directional control valve; and

FIG. 5 and 6 are further embodiments of an electromagnetic valve inaccordance with the principles of the present invention showing 3/2directional control valves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thereis located in a housing 2 made of magnetizable material the magnet coil3 in an insulated relationship with housing 2. Housing 2, together withthe magnet core 9 surrounded by coil 3, forms a magnetic return path 10into which there is embedded a sleeve 4 made of non-magnetic material.In the housing chamber 11 below magnetic return path 10, there aresituated armature plates 1 held by means of retaining clips 6. Armatureplates 1 have an annular central opening. It can be seen from FIG. 2that there are two trapezoidal armature plates resting against eachother at their bases and that a semicircular aperphragm spring 5, sothat the valve-closing member will be lifted from its seat and the valvewill be opened.

FIG. 3 shows an embodiment of a seat valve constructed in accordancewith this invention which is opened with the electromagnet beingdeenergized. A substantial number of parts of FIG. 3 are identical tothose of the seat valve of FIG. 1 and, therefore, like parts have beenassigned like reference numerals in both FIGS.

From housing chamber 11, a blind-end bore 20 extends into magnet core 9,the outlet 21 extending later.- ally from bore 20 through magneticreturn path 10. Before outlet 21 branches off from bore 20, a valve seat22 is disposed on a stepped portion of blind-end bore 20. In contrast tothe embodiment of FIG. 1, the positions of supporting member 13 and ofvalve body 7' jointed thereto are just reversed. The closing member ofvalve body 7' projects into blind-end bore 20 of magnet core 9, thuslying opposite valve seat 22. The inner edges of armature plates 1 gripthe under surface of collar 12 and are kept in position by means ofretaining clips 6 in the manner described with respect to FIG. 1. Withone end of diaphragm spring 5 engaging annular element 16 at collar 15'of supporting member 13' and with the other end of diaphragm spring 5engaging a groove in housing chamber- 11, the diaphragm spring ture iscut into each base. At the circular opening, the

inner edges of armature plates 1 grip the under surface of a collar 12of the supporting member 13 for the vvalve body 7. Supporting member 13is provided with clearance for motion by virtue of a centric recess 14in the magnet core 9 into which supporting member 13 is projecting. Atthe opposite end of axially symmetrical supporting member 13, a U-shapedcross-sectional annular element 16 is located on the top surface of acollar l5. Retaining clips 6 each have one end gripped by one arm ofannular element 16, while the other ends of clips 6 engage a groove inarmature plates 1. The inner edge of a star-shaped diaphragm spring 5includes a v 'closing member'resting against the valve seat of theoutlet 17 provided in the adjacent housing wall. Preferably, the samehousing wall also includes the inlet 18 terminating in housing chamber11. lnlet 18 is covered with a filter 8 to provide a protection againstdirt. A thread 19 provided at housing 2 permits the valve to be screwedinto a cooperating device such as a pressure medium conduit. If currentflows through coil 3 of the electromagnet, the induced magnetic fieldwill cause armature plates 1 to be attracted by magnet core 9 andmagnetic return path 10, respectively, armature plates 1 thus causingsupporting member 13 and the associated valve body 7 to follow againstthe force of dia- 5 via supporting member 13' keeps valve body .7 spacedapart from valve seat 22 and armature plates 1 apart from magneticreturn path 10. This embodiment also provides for a protective filter 8covering inlet 23 terminating in housing chamber 11.

In rest position,'when the valve is open, current flow through magnetcoil 3 will cause armature plates 1 and consequently supporting member13' and valve body 7' to be attracted so that the closing member of thevalve body 7 rests on its valve seat 22, thus interrupting theconnection between inlet and outlet.

In the two seat valves described above, the magnetic leakage field isreduced by virtue of magnetic return path 10, thus permitting moreefficient use to be made of the magnetic forces and consequentlyallowing utilization of a smaller electromagnet. The non-magnetic sleeve4 embedded in magnetic return path 10 avoids the occurrence of amagnetic short circuit and induces the lines of magnetic flux to runthrough armature plates 1. In order to prevent armature plates 1 fromfurther sticking to the magnet core following interruption of theenergizing current, a non-adhesive plate (not shown) made ofnon-magnetic material has been provided between magnet core 9 andarmature plates 1. Since it is known from experience that the adhesivesused did not stick, the non-adhesive plate, while resting on armatureplates 1 may be clamped under collar 12 of supporting member 13, or, inthe shape of an expanding cap, be squeezed into centric recess 14 ofmagnet core 9.

In contrast to a plunger-type armature, armature plates I enjoy theadvantage of moving under extremely low friction during switching and ofhaving less mass. In a valve constructed in accordance with the presentinvention, there is only one air gap in the magnetic circuit, namely,theworking air gap. The radial air gap necessary in frictionlesssuspended plunge r-type armatures in not required. The flat design ofthe armature also enables diaphragm springs to be mounted in apreferable manner. The diaphragm springs permit high forces to becontrolled more readily than is the case with spiral springs.

It has been proven that valves constructed in accordance with thepresent invention have very short switching times even if no specialmagnetic materials are used.

FIG. 4 shows the arrangement of the magnetic armature already describedtogether with a slide valve incorporating, in the embodiment shown,further decisive advantages particularly for use in antiskid controlsystems.

The housing of the slide valve contains a cylinder bore 30 enlarging atits one end to form a chamber 32 via a stepped portion 31. In its middlearea, cylinder bore 30 enlarges once more into a wide groove 33. Groove33 connects in its whole width with a port 34 of the slide valve.Cylinder bore 30 contains two slidably mounted pistons 36 and 37 coupledto each other via a mechanical connection 35. The diameter of piston 37is smaller than the diameter of piston 36. Piston 36 is sealed to theinner wall of cylinder bore 30 and projects into enlarged chamber 31.Piston 36 is secured against sliding out by means of a circlip 38. Bymeans of a recess provided in the lateral surface of piston 36, anannular chamber 39 is created permanently communicating with a secondport 40 of the slide valve. That end of piston 36 which is connectedwith the second piston 37 is reduced to the diameter of piston 37, thusproducing within the area of groove 33 a collar 41 on piston 36. Collar41 corresponding in length to the width of groove 33. The other end ofpiston 37 is tightly confined within cylinder bore 30 reduced to thediameter of piston 37. This diameter reduction of bore 30 createsannular chamber 42 communicating with the third port 43 of the 3/2directional control valve. The edges of groove 33 or of its port 34,respectively, together with the associated adjacent edges of collar 41on piston 36, form the leading edges 44 and 45 through which, undercommon sliding movements of pistons 36 and 37, groove 33 and thus port34 communicate with annular chamber 42 and the port 43, on the one hand,and with annular chamber 39 and port 40, on the other hand. At the endof piston 37 projecting out of cylinder bore 30, a first collar 46 isprovided resting against the housing when the valve is in rest position.A second collar 47 establishes the connection with the electromagneticcontrol system described above. In this FIG., also, like parts have beenassigned like reference numerals.

Housing 2 of the electromagnet is screwed into a recess of the valvecasing in which cylinder bore 30 terminates. The thus limited housingchamber 11 into which the end of the piston 37 projects, communicates,for the purpose of obtaining pressure balance, with the port 34 ofgroove 33 via a duct 48, and further with chamber 32 situated in frontof piston 36. The armature plates 1 with their inner edges grip theupper surface of collar 47 on the end of piston 37 and are secured bymeans of retaining clips 6 which are fixed to annular element 16. Theinner edge of diaphragm spring 5 also engages annular element 16 restingagainst collar 46 while the outer edges of spring 5 engage a groove ofhousing wall 2 of the electromagnet. Diaphragm spring 5 keeps botharmature plates 1 and pistons 36 and 37 in their illustrated home orrest positions.

As mentioned before, this valve is to be use preferably for antiskidcontrol systems. For this purpose, port 43 connects with the brakeactuation system, i.e., with the master cylinder, while port 34 connectswith the wheel brake cylinder and port 40 with the reservoir. In theevent of wheel locking danger, the electronic control system willtransmit a current pulse to the electromagnet. This pulse iscontinuously variable in accordance with the variation of the outputvariable relative to its rated value.

In the illustrated valve position, wherein the electromagnet isdeenergized, the brake can be operated as usual. The brake pressure istransmitted through port 43, annular chamber 42 and the port 34 to thewheel brake cylinder.

Pressure P, in the master cylinder is equal to pressure P, in the wheelbrake cylinder. Since pressure P via duct 48, also acts on the outerfront surfaces of pistons 36 and 37, these pistons are hydraulicallybalanced. If the electronic control unit of the antiskid system detectsdanger of wheel lock, current will flow through coil 3 of theelectromagnet and cause armature plates 1 to be attracted towardsmagnetic return path 10, thereby also moving the mechanically connectedpistons 36 and 37 in the same direction. In this process, leading edges44 first interrupt the pressure-medium connection between the mastercylinder and the wheel brake cylinder, whereupon the leading edges 45open the connection from port 34 of the wheel brake cylinder throughannular chamber 39 to port 40 leading to the reservoir, thus permittingpressure in the wheel brake to drop. Pressure P, of the master cylinderexerts the force P, X A on the annular surface A of collar 41 at piston36, whereas, caused by the flow conditions, pressure P, in the wheelbrake cylinder exerts the opposing force P 2 X A. Pressure P in thewheel brake cylinder is now continuously decreasing until the resultinghydraulic force (P, P X A acting on pistons 36 and 37 is equal to themagnetic force determined by the coil current, disregarding the frictionand spring forces. Variation of the coil current, which as mentionedabove is continuously variable dependent on the output variable,involves a change of the pressure difference P, P The characteristiccurve of the diaphragm spring 5 is preferably adapted to that of theelectromagnet in order to achieve independence of the resulting forcefrom the stroke and to obtain an improved controller action.

Thus, in a pressure regulator constructed in accordance with the presentinvention, the pressure difference between the brake control valve orthe master cylinder and the wheel brake cylinder is adjusted inproportion to the magnetic force. Via the coil current, the controlpressure thus represents a further item for the electronic control unit.

FIG. 5 shows a further improved embodiment of the slide valveconstructed in accordance with the present invention. This embodimentalso has one end of the cylinder bore 50 enlarged to form a chamber 51into which projects the tightly confined smaller piston 52. Piston 53,which is of larger diameter than piston 52, is confined within that areaof cylinder bore 50 enlarged by a stepped portion and rests against theadjacent surface of piston 52, around which end an annular chamber 54 isformed. By means of a recess provided in the lateral surface of piston53, an annular chamber 55 is created permanently communicating with oneport 56 which, when used in an antiskid control system. leads to thereservoir. A further recess provided in bore creates anannular chamber57. A collar 58 is provided on piston 53 having a width to the width ofa groove 59. This groove 59 connects with the second port 60 of thevalve,.which port leads to the wheel brake cylinder. The edges of groove59, together with the associated adjacent edges of collar 58, form theleading edges 61 and 62 of the slide valve. The annular chamber 57communicates with chamber 11 via recesses 63 provided in the valvehousing. Chamber 11 receives piston 53 which is connected with theelectromagnetic control system in the manner described with reference toFIG. 4. Via one of these recesses 63, the annular chamber 57 and chamber11 communicate by means of a duct 64 with chamber 51 and the port 65leading to themaster cylinder, in order to achieve pressure balance. Thegroove 59 connects with the annular chamber 54 at the piston 52 via alongitudinal bore 66 and a cross bore 67 provided in piston 53.

Basically, the mode of operation of the embodiment of FIG. 5 is the sameas that described with reference I to FIG. 4. In addition, theembodiment of FIG. 5 has the following advantages.

The pistons are interchanged and pressure P of the master cylinderalways acts on the outer end surfaces of pistons 52 and 53, whilepressure P of the wheel brake cylinder acts on the inner end surfaces ofpistons 52 and 53. This avoids the necessity for providing a mechanicalmeans for connecting the pistons. Therefore, when the magnet isenergized only the friction forces of piston 53 have to be overcome andpiston 52 is made to follow hydraulically by virtue of pressure P of themaster cylinder.

FIG. 6 represents a slide valve operating according to the sameprinciples as described above but showing a further simplifiedembodiment provided with an integrally formed valve slide. In the valvecasing 70, there is accommodated the cylinder 71 with the cylinder bore72. The valve slide is tightly and slidably received in cylinder bore 72terminating in the housing chamber 74 which communicates with the mastercylinder via a port 73. A recess 76 provided in the wall of cylinder 71connects cylinder bore 72 with a further housing chamber 77 whichcommunicates with the wheel brake cylinder via a port 78. The collar 79is produced by a recess in valve slide 75. The width of collar 79corresponds to the width of recess 76 provided in the cylinder wall.Those edges of collar 79 and recess 76 which are adjacent to each otherform the leading edges 80 and 81 of the valve. The annular chamber 82 iscreated by the above-mentioned recess in valve slide 75 and communicateswith the housing port 84 via a cross bore 83 in the cylinder wall. Port84 leads to the reservoir. Cylinder 71 projects into a housing chamber85 into which is screwed housing 86 of the electromagnet. Valve slide 75connects with the pressure-balanced magnetic armature 87 and is biasedin rest position by means of a spring 88. Via a duct 89 provided invalve casing,70, housing chamber 77 is connected with housing chamber 85containing the valve-slide front surface facing the electromagnet. Inthis way, valve slide 75 is pressure-balanced'in rest position. Brakepressure is thus free to be transmitted from the master cylinder throughhousing chamber 74, cylinder bore 72, recess 76 in the cylinder wall,and housing chamber 77, to the wheel brake cylinder. If theelectromagnet receives a current pulse in the event of wheel lockingdanger, magnetic armature 87 will be attracted towards the magnet core90, with the valve slide 75 being displaced. Leading edges 80 firstinterrupt the pressure-medium connection between the master cylinder andthe wheel brake cylinder, whereupon leading edges 81 will open up theconnection between wheel brake cylinder and reservoir. The mastercylinder pressure P acts on the front surface of collar 79 of the valveslide 75, while, via duct 89, the wheel brake cylinder pressure P actson the front surface of valve slide 75 facing the electromagnet. Asdescribed above, a pressure difference is then produced at valve slide75 which is proportional to the continuously variable coil current. Withthe magnet force being of the same magnitude, the crosssectional area ofthe valve slide in FIG. 6 is bound to be approximately the same as theannular surface A in FIG. 4.

It is to be understood that the functional aspects of the pressureregulating valve described herein are not limited to the inventiveconstruction of an electromagnet embodying armature plates. Therefore,FIG. 6 shows an embodiment of the invention incorporating a plunger-typearmature.

It is to be understood further that the advantages mentioned inconnection with the description of the seat valves of FIGS. 1 and 2 andrelating to the special arrangement of the armature plates also refer toslide valves. These advantages consist in affording valveslide movementunder extremely low friction during switching, a small mass of thearmature, the omission of the radial air gap with the magnetic armaturebeing mounted under a minimum amount of friction, and the possibility ofusing diaphragm springs.

It is in the particular use in antiskid systems that the slide valves ofFIGS. 4, 5 and 6 include still further decisive advantages. There isfirstly, as has already been mentioned previously, the pressuredifference between the brake control valve and, respectively, the mastercylinder and the wheel brake cylinder, which difference is continuouslyvariable in proportion to the magnet current. Since 3/2 directionalcontrol valves 'are used, each control circuit requires but one valve.The phase in the antiskid control cycle during which the pressure ismaintained at a constant value and which had to be created in 3/2directional control valves by clicking, poses no problems in slidevalves. The valve constructed in accordance with this invention providesfor more freedom in selecting the most expedient control method and is,among other things, the prerequisite for a continuous control system nolonger producing sharply defined phases for pressure decrease, pressurestabilization and pressure increase, but producing a pressure curvesmoothly swinging near its ideal value. This is achieved by permanentlyinterrogating the output variable in a timing screen and by modifyingthe coil current of the electromagnet according to the variationexceeding the permissible deviation with a downward or upward tendency.Thus, the invention relates to an analog valve instead of a digitalvalve, i.e., control is via the current intensity and not via theduration of voltage application.

In the valves of FIGS. 4, 5 and 6, the steepness of the curve slopes(dp/dt) is not predetermined as is the case with seat valves, butvariable. The pressure decrease A p is not ignored, since the pressurecontrolled by the brake control valve (master cylinder) also plays agoverning role.

Since the pistons or slides, respectively, are hydraulically balanced innormal or rest position, only the friction forces and the small springforce have to be overcome when switching on. This results in shortresponse times. The slide valves combine the advantage of low resistanceto flow with accurate control possibilities. thus enabling the valves tobe installed directly in the brake line.

While we have described above the principles of our invention inconnection with specific apparatus, it is to be clearlly understood thatthis description is made only by way of example and not as a limitationto the scope of our invention as set forth in the objects thereof and inthe accompanying claims.

We claim:

1. An electromagnetic valve for use in an antiskid brake systemcomprising:

a magnet housing having a first longitudinal axis;

a magnet winding disposed in said housing coaxial of said axis;

a magnetic return path disposed in said magnet housing magneticallycoupled to said winding;

a sleeve of non-magnetic material disposed in said return path coaxialof said first axis;

a first chamber disposed in said magnet housing adjacent said sleeve andsaid return path;

a valve body disposed coaxial of said first axis, at least a portion ofsaid valve body projecting into said first chamber;

a plurality of armature plates disposed in said first chamber, saidarmature plates having a central opening coaxial of said axis, the outeredges of said armature plates abutting said return path and beingslightly'inclined away from said return path, and the inner edges ofsaid armature plates engaging said portion of said valve body projectinginto said first chamber to move said valve body when said winding isenergized and said armature plates adjacent said inner edges areattracted toward said return path;

a spring disposed in said first chamber in an engaged relationship withsaid valve body and said armature plates to bias said valve body andsaid armature plates in a rest position;

said valve body controlling the flow of a brake pressure medium throughsaid valve between at least a brake pressure medium inlet and a brakepressure medium outlet when said winding is energized and said armatureplates are attracted toward said return path;

said spring including a diaphragm spring having openings therethroughand a central aperture coaxial of said first axis,

the inner edge of said diaphragm spring adjacent said central apertureengaging a groove provided in said portion of said valve body projectinginto said first chamber and the outer edge of said diaphragm springbeing firmly connected to said magnet housing surrounding said firstchamber. 2. A valve according to claim 1, wherein said groove isprovided by a U-shaped crosssectioned annular element mounted on saidportion of said valve body projecting into said first chamber. 3. Avalve according to claim 2, wherein said diaphragm spring is starshaped. 4. A valve according to claim 3, wherein the characteristiccurve of said diaphragm spring is adapted to the characteristic curve ofan electromag ne t including said winding, said return path, said sleeveand said armature plates. 5. A valve according to claim 4, furtherincluding a valve housing connected to said magnet housing,

said valve housing havig a second longitudinal axis which is anextension of said first axis; a pressure medium source inlet connectionextending through the wall of said valve-housing; a pressure mediumreservoir outlet connection extending through the wall of said valvehousing; and a pressure medium wheel brake cylinder outlet connectionextending through the wall of said valve housing; and wherein said valvebody includes a valve slide extending from said first chamber into saidvalve housing coaxial of said second axis, said valve slide beingdisposed in a cooperative relationship with said source inletconnection, said reservoir outlet connection and said wheel brakecylinder outlet connection to control the flow of pressure mediumbetween these three connections, said valve slide being pressurebalanced in its rest position when the flow of pressure medium isbetween said source inlet connection and said wheel brake cylinderoutlet connection. 6. A valve according to claim 5, further including asecond chamber disposed in said valve housing embracing the end of saidvalve slide remote from said first chamber; and a duct disposed in saidvalve housing to interconnect said first and second chambers. 7. A valveaccording to claim 6, wherein said duct is connected to said wheel brakecylinder outlet connection. 8. A valve according to claim 6, whereinsaid duct is connected to said source inlet connection. 9. A valveaccording to claim 6, wherein said valve slide is formed by two pistonsin tandem relationship. 10. A valve according to claim 9, wherein saidtwo pistons are mechanically connected together, said two pistons beingpressure-balanced in their rest position by the pressure present at saidwheel brake cylinder outlet connection being applied to the remote endsof said two pistons and by the pressure at said source inlet connectionbeing applied to the adjacent ends of said two pistons. 11. A valveaccording to claim 9, wherein said two pistons can move freely withrespect to each other, said two pistons being pressure-balanced in theirrest position by the pressure at said source inlet connection beingapplied to the remote ends of said two pistons and by the pressure atsaid wheel brake cylinder outlet connection being applied to theadjacent ends of said two pistons. 12. A valve according to claim 6,wherein when said winding is energized to provide a magnetic force saidvalve slide is actuated in a direction opposite to that of said magneticforce by pressure from said source inlet connection being applied to 1 112 a first actuating surface and is actuated inthe di- 14, A valveaccording to claimlZ, wherein Tecilon' of Sald magnenc force; y P u fromI a current energizing said winding and consequently said wheel brakecylinder outlet connection being applied to a second actuating surface.13. A v alv e according to claim 12, wherein D said first and second.actuating surfaces are equal in connection are comlnuously VariablesizeI i the pressure difference between said source inlet connection andsaid wheel brake cylinder outlet

1. An electromagnetic valve for use in an antiskid brake systemcomprising: a magnet housing having a first longitudinal axis; a magnetwinding disposed in said housing coaxial of said axis; a magnetic returnpath disposed in said magnet housing magnetically coupled to saidwinding; a sleeve of non-magnetic material disposed in said return pathcoaxial of said first axis; a first chamber disposed in said magnethousing adjacent said sleeve and said return path; a valve body disposedcoaxial of said first axis, at least a portion of said valve bodyprojecting into said first chamber; a plurality of armature platesdisposed in said first chamber, said armature plates having a centralopening coaxial of said axis, the outer edges of said armature platesabutting said return path and being slightly inclined away from saidreturn path, and the inner edges of said armature plates engaging saidportion of said valve body projecting into said first chamber to movesaid valve body when said winding is energized and said armature platesadjacent said inner edges are attracted toward said return path; aspring disposed in said first chamber in an engaged relationship withsaid valve body and said armature plates to bias said valve body andsaid armature plates in a rest position; said valve body controlling theflow of a brake pressure medium through said valve between at least abrake pressure medium inlet and a brake pressure medium outlet when saidwinding is energized and said armature plates are attracted toward saidreturn path; said spring including a diaphragm spring having openingstherethrough and a central aperture coaxial of said first axis, theinner edge of said diaphragm spring adjacent said central apertureengaging a groove provided in said portion of said valve body projectinginto said first chamber and the outer edge of said diaphragm springbeing firmly connected to said magnet housing surrounding said firstchamber.
 2. A valve according to claim 1, wherein said groove isprovided by a U-shaped cross-sectioned annular element mounted on saidportion of said valve body projecting into said first chamber.
 3. Avalve according to claim 2, wherein said diaphragm spring is starshaped.
 4. A valve according to claim 3, wHerein the characteristiccurve of said diaphragm spring is adapted to the characteristic curve ofan electromagnet including said winding, said return path, said sleeveand said armature plates.
 5. A valve according to claim 4, furtherincluding a valve housing connected to said magnet housing, said valvehousing havig a second longitudinal axis which is an extension of saidfirst axis; a pressure medium source inlet connection extending throughthe wall of said valve housing; a pressure medium reservoir outletconnection extending through the wall of said valve housing; and apressure medium wheel brake cylinder outlet connection extending throughthe wall of said valve housing; and wherein said valve body includes avalve slide extending from said first chamber into said valve housingcoaxial of said second axis, said valve slide being disposed in acooperative relationship with said source inlet connection, saidreservoir outlet connection and said wheel brake cylinder outletconnection to control the flow of pressure medium between these threeconnections, said valve slide being pressure balanced in its restposition when the flow of pressure medium is between said source inletconnection and said wheel brake cylinder outlet connection.
 6. A valveaccording to claim 5, further including a second chamber disposed insaid valve housing embracing the end of said valve slide remote fromsaid first chamber; and a duct disposed in said valve housing tointerconnect said first and second chambers.
 7. A valve according toclaim 6, wherein said duct is connected to said wheel brake cylinderoutlet connection.
 8. A valve according to claim 6, wherein said duct isconnected to said source inlet connection.
 9. A valve according to claim6, wherein said valve slide is formed by two pistons in tandemrelationship.
 10. A valve according to claim 9, wherein said two pistonsare mechanically connected together, said two pistons beingpressure-balanced in their rest position by the pressure present at saidwheel brake cylinder outlet connection being applied to the remote endsof said two pistons and by the pressure at said source inlet connectionbeing applied to the adjacent ends of said two pistons.
 11. A valveaccording to claim 9, wherein said two pistons can move freely withrespect to each other, said two pistons being pressure-balanced in theirrest position by the pressure at said source inlet connection beingapplied to the remote ends of said two pistons and by the pressure atsaid wheel brake cylinder outlet connection being applied to theadjacent ends of said two pistons.
 12. A valve according to claim 6,wherein when said winding is energized to provide a magnetic force saidvalve slide is actuated in a direction opposite to that of said magneticforce by pressure from said source inlet connection being applied to afirst actuating surface and is actuated in the direction of saidmagnetic force by pressure from said wheel brake cylinder outletconnection being applied to a second actuating surface.
 13. A valveaccording to claim 12, wherein said first and second actuating surfacesare equal in size.
 14. A valve according to claim 12, wherein a currentenergizing said winding and consequently the pressure difference betweensaid source inlet connection and said wheel brake cylinder outletconnection are continuously variable.